(1) Field of the Invention
The present invention relates to a linear compressor for reciprocating a piston fitted in a cylinder by a linear motor to draw in, compress and discharge gas.
(2) Description of the Prior Art
In refrigeration cycle, HCFC refrigerants such as R22 are stable compounds and decompose the ozone layer. In recent years, HFC refrigerants begin to be utilized as alternative refrigerants of HCFCs, but these HPC refrigerants have the nature for facilitating global warming. Therefore, a study is started to employ HC refrigerants which do not decompose the ozone layer or largely affect global warming. However, since this HC refrigerant is flammable, it is necessary to prevent explosion or ignition so as to ensure safety. For this purpose, it is required to reduce the amount of refrigerant to be used as small as possible. On the other hand, the HC refrigerant itself does not have lubricity and is easily melted into lubricant. For these reasons, when the HC refrigerant is used, an oilless or oil pure compressor is required. A linear compressor in which a load applied in a direction perpendicular to an axis of its piston is small and a sliding surface pressure is small is known as a compressor which can easily realize oilless as compared with a reciprocal type compressor, a rotary compressor and a scroll compressor.
However, in the case of the linear compressor also, a sliding degree of the sliding surfaces between the cylinder and the piston affects the efficiency and durability of the linear compressor. Therefore, considerably complicated means is required for constituting an oilless linear compressor.
For example, U.S. Pat. No. 5,920,133 discloses a Stirling engine in which a pair of leaf springs are disposed on opposite ends of a linear motor, and a piston is slidably supported by the leaf springs. With this structure, even if a force for inclining the piston is applied to the piston by magnetic attraction force generated by the linear motor, the piston is less prone to be displaced in a diametrical direction thereof.
However, this structure has a problem that since the piston is disposed outside the pair of spring members, a moving member constituting the linear motor becomes longer in its axial direction, and it is difficult to reduce the linear motor in size.
On the other hand, in order to shorten the axial size, there is a linear motor in which a compression chamber is defined by disposing the spring member only on the opposite side of the compression chamber and utilizing an inner space of the linear motor.
With this structure, however, since the piston is supported only by the spring member on the opposite side of the compression chamber, a displacement of the piston in its diametrical direction is great, and a pressure on sliding surfaces of the piston and the cylinder is increased. Further, there is a problem that since the compression chamber is disposed in the vicinity of the linear motor, the compression chamber is prone to receive heat of the linear motor.
In view of the above circumstances, it is an object of the present invention to provide a high-efficiency linear compressor in which even if a compression chamber is defined utilizing an inner space of the linear motor to reduce its size, an amount of heat transmitted from the linear motor to the compression chamber can be reduced by forming a space between the linear motor and a cylinder which defines the compression chamber.
Further, it is another object of the invention to provide a linear compressor in which even if magnetic attraction force generated by a linear motor is applied to the piston, a pressure on sliding surfaces of the piston and the cylinder is prevented from being increased and the linear compressor can be reduced in size by supporting opposite ends of the piston by spring members disposed on the opposite ends of the linear motor through a connecting member.
To achieve the above objects, according to a first aspect of the present invention, there is provided a linear compressor comprising a cylinder having a flange and a cylindrical portion supported in a hermetic vessel by a support mechanism, a piston movably supported in the cylindrical portion along an axial direction thereof, a spring member applying an axial direction to the piston, and a linear motor having a stator fixed to the flange of the cylinder and disposed around an outer periphery of the cylindrical portion and a moving member coupled to the piston, wherein a space is formed between the stator and the cylindrical portion.
With the first aspect, since the space is formed between the stator and the cylindrical portion, heat from the linear motor is less prone to be transmitted to the refrigerant in the compression chamber defined in the cylinder, heat-receiving loss of the linear compressor is reduced and its efficiency is enhanced.
According to a second aspect of the invention, in the linear compressor of the first aspect, the linear compressor further comprises a communication path which brings the space and outer peripheral regions of the cylinder and the linear motor.
With the second aspect, since the refrigerant in the space causes convection without being deposited, the heat-receiving loss is further reduced.
According to a third aspect of the invention, in the linear compressor of the second aspect, the communication path is formed in the flange. With the third aspect, high-temperature refrigerant in the space can efficiently be discharged to the outer peripheral regions of the cylinder and the linear motor and thus, the heat-receiving loss can be reduced.
According to a fourth aspect of the invention, there is provided a linear compressor comprising a cylinder having a flange and a cylindrical portion supported in a hermetic vessel by a support mechanism, a piston movably supported in the cylindrical portion along an axial direction thereof, a linear motor having a stator fixed to the flange of the cylinder and disposed around an outer periphery of the cylindrical portion and a moving member coupled to the piston, and a pair of spring members respectively disposed in the vicinity of the opposite ends of the linear motor and applying axial forces to the piston, wherein a space is formed between the stator and the cylindrical portion, and a communication member for bringing the moving member and the spring member closer to the flange is disposed in the space. With this arrangement, the heat from the linear motor is less prone to be transmitted to the refrigerant in the compression chamber defined in the cylinder, and the linear compressor can be reduced in size as compared with that of the first embodiment.
According to a fifth aspect of the invention, in the linear compressor of the first or fourth aspect, the spring member comprises a substantially C-shaped plate, the plate is disposed such that a distance between one end of the plate to a phantom center thereof is different from a distance between the other end of the plate to the phantom center. When the spring members are press-formed, if the spring members are integrally formed into complicated shape, it is necessary to secure punching margins between the resilient portions. However, by dividing the resilient portions of the spring members into the substantially C-shaped plates and combining the plates, it is unnecessary to secure punching margins between the resilient portions, and a width of each plate of the resilient portion can be increased correspondingly. With this design, it is possible to enhance the strength of the spring members.
According to a sixth aspect of the invention, in the linear compressor of the fifth aspect, the plates are combined. By dividing the resilient portions of the spring members into the substantially C-shaped plates and combining the plates, it is unnecessary to secure punching margins between the resilient portions, and a width of each plate of the resilient portion can be increased correspondingly.
According to a seventh aspect of the invention, in the linear compressor of the fifth aspect, one end of the plate disposed closer to the phantom center is fixed to the moving member, and the other end of the plate is fixed to the stator. Therefore, a width of the resilient portion can be increased.
According to an eighth aspect of the invention, in the linear compressor of the fourth aspect, the spring members include a plurality of resilient portions spirally extending in a circumferential direction from a center, the pair of spring members are disposed and fixed such that extending directions of the resilient portions from the center are different from each other. With this arrangement, the directions of the diametrical displacement forces of the spring members do not coincide with each other, the diametrical displacement of the connected spring members can be reduced and thus, the sliding surface pressure between the outer peripheral surface of the piston and the inner peripheral surface of the cylinder can further be reduced. Therefore, mechanical loss of the linear compressor is reduced, its efficiency is enhanced, and the reliability is also enhanced.
According to a ninth aspect of the invention, in the linear compressor of the fourth aspect, the connecting member is made of non-magnetic material. Therefore, even if the connecting member reciprocates in the leaking magnetic field in the vicinity of the linear motor, iron loss such as eddy current is not generated, and this can contribute the enhancement of the efficiency of the linear compressor.
According to a tenth aspect of the invention, in the linear compressor of the fourth aspect, the connecting member is provided with a plurality of slits along its moving direction. Therefore, even if the connecting member reciprocates in the leaking magnetic field in the vicinity of the linear motor, iron loss such as eddy current is not generated, and this can contribute the enhancement of the efficiency of the linear compressor.